I haven't used one as of yet, but I can't see it being all that fancy. It's an expensive heavy flamer that, if you're really lucky, will blow up and take a few more baddies out with it.
Interesting in that it's basically a suicide bomber... that's a KP nightmare (possibly enough to keep it out of lists)... though I don't think it does the job all that well.
The flamer is decent against MEQ in general coverage, but the more models in the unit, the more models you'll hit... however swarmy types will typically be able to take away its measly 2 T4 wounds before any sort of power fist has the chance to swat it (giving it a chance to go boom). Even then, the resulting boom is questionable (though also potentially hilarious).
Perhaps a squad of them in a spore would make the enemy think twice about bunching up into cover (to protect from our sad lack of offensive grenades)... in which case taking one cheap-enough sluff unit may be worth it. Though it still eats an Elite slot, which is highly regarded these days.
We'll see...
Khira'lyth